1. Field of the Invention
The present invention relates generally to enclosures deployed in fiber optic communications networks, and more particularly, to a factory-assembled installation closure having apparatus for routing, securing and protecting preterminated and/or connectorized optical fibers branched or withdrawn from a fiber optic distribution cable at a mid-span access location.
2. Technical Background
Optical fiber is increasingly being used for a variety of broadband applications including voice, video and data transmissions. As a result of the ever-increasing demand for broadband communications, fiber optic networks typically include a large number of mid-span access locations at which one or more optical fibers are branched or withdrawn from a distribution cable. These mid-span access locations provide multiple dedicated fiber drops to connect a plurality of subscribers to the network. Thus, mid-span access locations are used to extend an “all optical” communications network to commercial and residential subscribers. In this regard, fiber optic networks are being developed that deliver “fiber-to-the-curb” (FTTC), “fiber-to-the-business” (FTTB), “fiber-to-the-home” (FTTH), or “fiber-to-the-premises” (FTTP), referred to generically as “FTTx.” Based on the increase in the number of access points and the unique physical attributes of the optical fibers themselves, enclosures are needed for routing, securing and protecting optical fibers at the access points during and after installation of the distribution cable. Such enclosures are also needed for providing access to the preterminated and/or connectorized optical fibers, while at the same time providing protection for the access point from exposure to adverse environmental conditions. At the same time, however, these enclosures must not prevent the fiber optic distribution cable from being deployed through small diameter conduits or over conventional sheave wheels, rollers and pulleys.
In one example of a fiber optic communications network, one or more drop cables are interconnected with a distribution cable at a mid-span access location within an aerial splice closure suspended from an aerial strand or from the distribution cable itself. Substantial expertise and experience are required to configure the optical connections within the closure in the field. In particular, it is often difficult to enter the closure and to identify an optical fiber of the distribution cable to be interconnected with an optical fiber of a particular drop cable. Once identified, the optical fibers of the drop cables are typically joined directly to the optical fibers of the distribution cable at the mid-span access location using conventional splicing techniques, such as fusion splicing. In other instances, the optical fibers of the drop cables and the optical fibers of the distribution cable are first spliced to a short length of optical fiber having an optical connector mounted on the other end, referred to in the art as a “pigtail.” These pigtails are then routed to opposite sides of a connector adapter sleeve located within the closure to interconnect the drop cable with the distribution cable. In either case, the process of entering and configuring the closure is not only time consuming, but frequently must be accomplished by a highly skilled field technician at significant cost and under field working conditions that are less than ideal. Reconfiguring optical fiber connections in an aerial splice closure is especially difficult, particularly in instances where at least some of the optical fibers of the distribution cable extend uninterrupted through the closure, since the closure cannot be readily removed from the distribution cable. Further, once the optical connections are made, it is often labor intensive, and therefore costly, to reconfigure the existing optical connections or to add additional optical connections.
In order to reduce costs by permitting less experienced and less skilled technicians to perform mid-span access optical connections and reconfigurations in the field, communications service providers are increasingly pre-engineering fiber optic networks and demanding factory-prepared interconnection solutions, commonly referred to as “plug-and-play” type systems.
In response, fiber optic hardware and equipment manufacturers have developed several approaches to overcome the disadvantages of accessing and splicing optical fibers in the field. In one such approach, drop cables are spliced to the distribution cable in the factory during manufacturing. While advantageous for manufacturing high quality access points in an environmentally controlled factory environment, disadvantages include the relatively large size (e.g., diameter) and inflexibility of the distribution cable assembly at the access points, as well as the incremental cost associated with dormant drop cables. Most importantly, factory-attached drop cables may not always be able to mitigate misplacement of the access location due to inaccurate pre-engineering measurements or installation errors since the drop cables are configured with predetermined lengths. As such, the current approaches do not completely address the communications service provider's need to reduce installation and deployment costs.
Accordingly communications service providers continue to desire low-profile, factory assembled “plug-and-play” closure solutions which can be installed and deployed using existing equipment and methods and which require a minimum amount of field labor for performing interconnections. It would be desirable to provide an installation closure assembly for routing, securing and protecting preterminated and connectorized optical fibers branched or withdrawn from a fiber optic distribution cable at a pre-engineered mid-span access location. It would also be desirable to provide a closure for an FTTx network that may be readily reconfigured after installation, such that drop cables may be quickly and easily interconnected at the access location. Further, it would be desirable to factory-assemble the closure on the distribution cable at the respective mid-span access locations with the lowest possible profile (i.e., outer diameter), while maintaining access to the optical fibers branched or withdrawn from the distribution cable.